The present invention relates to the analyzation and/or measurement of residual amounts of specific chemical species within a working fluid system. Residual analyzers are typically adapted to measure such chemicals as free chlorine, total chlorine, potassium permanganate or chlorine dioxide within a working fluid and may be applied to such commercial applications as drinking water, waste water, and reactor cooling water. The present invention relates to both a residual analyzer type probe and a working fluid sampler system.
A number of analytical methods may be employed for the determination of specific chemical species within a working fluid. Three of these analytical methods include amperometry, colorimetry and potentiometry. Each of these methods has its limitations and advantages for specific applications. The typical commercial applications involving drinking water and the like often utilize amperometry or potentiometry.
A typical amperometric type probe includes two electrodes having an applied potential across the electrodes. Under ideal conditions, the current produced within the probe is proportional to the concentration of the chemical species that is oxidized and reduced at the electrodes. Therefore, zero concentration of the species within the working fluid should result in no current being produced. In actual use, however, variations in conductivity, pH, temperature, electropotential, interfering substances and electrode and flow fouling may cause significant errors, especially at low residuals (typically below 0.1 mg/l). Liquid or gas reagents are often utilized in such low residual applications for conditioning the working fluid. Means for temperature compensation and the use of applied potentials are also known methods of minimizing the errors associated with this type analyzation. However, a probe utilizing these various means of compensation for the changing characteristics of the working fluid will still require periodic zero calibration for proper continuous operation.
A more recent approach in commercial amperometric type probes includes the utilization of a membrane to isolate the electrodes from the working fluid. The membrane is positioned between the fluid and the electrodes and protects the electrodes from ionized substances while maintaining a stable electrochemical condition at the electrodes. This type structure typically results in a near true and stable zero calibration. However, due to the reduced sensitivity created by the membrane, varying diffusion rates for different species through the membrane and frequent membrane fouling, this type structure is often considered inadequate for the analyzation of reactor cooling water and waste water.
Sensitivity of the probe used in making the residual measurements is a significant factor in the commercial applicability of a probe assembly to a specific working fluid. Other operational factors, however, must also be considered in evaluating the overall cost of a continuous system. A typical residual analyzer probe which includes a membrane, although inaccurate in cooling water and waste water applications, often reduces operating costs since reagents are not required to condition the working fluid. Reagents are often required for accurate operation of a probe having exposed electrodes without membrane protection. Additionally, reagents are utilized with non-membrane type probes to maintain electrode cleanliness during its continuous operation. The amount of reagents required as well as their effect on the working fluid are often significant considerations in many commercial applications.